Photoluminescent printed waveguides can be produced using various photoluminescent colorants which are transparent when non-energized, yet emit color when subjected to ultra-violet, violet, or blue light energy. By printing on clear waveguides, multiple waveguide layers can be stacked and alternately energized to produce engaging motion effects. This technology has the benefit over competing technologies such as LCD in that it is a low cost printed approach which can be produced in sizes and shapes other than the standard ratio rectangular LCD products. Unlike LCDs, it can also be contour cut or 3D formed.
With emissive phosphors, it is impossible to create darkness. Primary RGB colors combine to form white. Therefore, provision of a dark background for image contrast is needed. This background can be provided by a dark ambient background such as in a dimly lit room, or by placing a dark surface behind the photoluminescent printed panels.
Photoluminescent inks often fade due to excitation such that useful life is greatly limited. Inclusion of motion, light or sound sensors to activate the display only when customers are present is one way to extend life, yet this approach has the drawback of being non-activated when customers are not in immediate proximity. Many display owners desire display systems which have at least 1 layer visible during non-sensor activated periods so that their customers who may be beyond the sensor activation range can still be presented with effective content.
Additionally, some photoluminescent colorants are not perfectly transparent. In ambient light, even when not intentionally subjected to ultra-violet, violet, or blue excitation light, these colorants can still exhibit noticeable color. When an image, text, or a graphic element is placed behind such a semi-transparent photoluminescent printed layer(s), a slight discoloration is imparted on the posterior layer.
In photoluminescent printed waveguides, excitation light is consumed by the presence of phosphors. As the quantity of phosphors increases, so does the requirement for excitation energy. It can be said that a waveguide absent of any photoluminescent phosphors requires no excitation energy and will emit no light. The opposite can also be stated. Complete coverage of a waveguide with RGB photoluminescent phosphors requires the most energy and, if balanced, produces white light. In practice, producing a largely white emissive display consumes much more energy than a dark one. Furthermore, light consumption across a waveguide decays so that available energy from the light injection point drops off sharply moving into the waveguide. This places practical limits the amount of photoluminescent ink which can be excited, and hence restricts the kind of artwork which can be used. It also is the primary limiting factor restricting the size of such waveguide displays.
Emissive RGB printed waveguides dependent on total internal reflection which convert incident energy of one wavelength to emissive color, consume available excitation energy according to the quantity and location of printed RGB phosphors. As the quantity of phosphors increase, the required excitation light must also increase. Therefore in general, dark background artwork is preferred over white background artwork. However many customer's require imagery, text or graphic elements containing a large quantity of light colored features such as graphics against a white background or imagery of snow filled mountains or images of white colored or near white colored products.